Surfactant-based products such as body washes, shampoos, dishwashing detergents, laundry detergents, and automotive detergents, among others, are often thickened by utilizing high concentration of surfactants, by combining viscosity synergistic surfactants, or by combining the surfactants with small amounts of salts, such as sodium salts. These formulations result in high viscosity products that appear rich and smooth but they are limited in that they do not provide sufficient low shear viscosity to allow for suspension of particles. Such particulates might include aesthetic agents (decorative beads, pearlescents, air bubbles, fragrance beads, etc.) or active ingredients (insoluble enzymes, encapsulated actives such as moisturizers, zeolites, exfoliating agents (e.g. alpha hydroxyl and/or glycolic acids or polyethylene beads), vitamins (e.g. vitamin E)) etc. or both.
Conventional thickeners and suspension aids such as xanthan gum, carboxymethyl cellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropylmethylcellulose (HPMC), and many types of polyacrylates do not function well in surfactant-thickened systems and often lead to a loss of transparency due to clouding, gelling, and/or phase separation or lack sufficient suspension properties. For example, xanthan gum imparts excellent suspension properties in certain body wash formulations with low surfactant-thickening but the gum often loses its suspension ability in systems with high surfactant thickening, usually resulting in a hazy, irregular appearance, and a grainy or lumpy texture. Cellulosic products (CMC, HEC, HPMC, etc.), as another example of conventional thickeners, provide unreliable suspension and have significant limitations with respect to surfactant compatibilities. Acrylates systems are common, however, these systems do not always achieve a sufficient clarity level, require high concentrations of polymer, and are not considered natural. Salts are often capable of increasing high shear viscosity in surfactant-thickened systems but do not impart long-term suspension ability.
There is presently a desire in the consumer products industry to provide for transparent surfactant-thickened systems with particulates suspended therein, as well as a suspension aid for high surfactant systems where many alternative thickeners will not function.
It has been discovered that microfibrous cellulose (MFC), bacterially derived or otherwise, can be used to provide suspension of particulates in surfactant-thickened systems as well as in formulations with high surfactant concentrations. It was also discovered that the MFC may be used for this purpose with or without co-agents. When bacterially-derived microfibrous cellulose is utilized, cellular debris can be eliminated which results in transparent solutions at typical use levels.
The microfibrous cellulose appears unaffected by the surfactant micelle development and maintains good suspension in these systems. Microfibrous cellulose is unique in its ability to function in these systems in large part because it is dispersed rather than solubilized, thereby achieving the desired suspension properties in formulations that would otherwise display the hazing and/or precipitation often seen using alternative solubilized polymers.